The process of domestication has led to dramatic morphological and physiological changes in crop species due to
adaptation to cultivation and to the needs of farmers. To investigate the phenotypic architecture of shoot- and rootrelated
traits and quantify the impact of primary and secondary domestication, we examined a collection of 36 wheat
genotypes under optimal and nitrogen-starvation conditions. These represented three taxa that correspond to key steps
in the recent evolution of tetraploid wheat (i.e. wild emmer, emmer, and durum wheat). Overall, nitrogen starvation
reduced the shoot growth of all genotypes, while it induced the opposite effect on root traits, quantified using the
automated phenotyping platform GROWSCREEN-Rhizo. We observed an overall increase in all of the shoot and root
growth traits from wild emmer to durum wheat, while emmer was generally very similar to wild emmer but intermediate
between these two subspecies. While the differences in phenotypic diversity due to the effects of primary domestication
were not significant, the secondary domestication transition from emmer to durum wheat was marked by a large and
significant decrease in the coefficient of additive genetic variation. In particular, this reduction was very strong under
the optimal condition and less intense under nitrogen starvation. Moreover, although under the optimal condition both
root and shoot traits showed significantly reduced diversity due to secondary domestication, under nitrogen starvation
the reduced diversity was significant only for shoot traits. Overall, a considerable amount of phenotypic variation was
observed in wild emmer and emmer, which could be exploited for the development of pre-breeding strategies.